Molded Balsa Parts -- Strength vs Weight

I've got three turtle decks molded for my 'Zoot Suit' Nobler (the object of which is to be as light as possible, among others).

Deck one is 3/32 Balsa formed directly over the mold. It is the flimiest and weighs .180 Oz.

Deck two is two layers of 1/32 balsa with a layer of .005 carbon fiber mat in between, fixed with aerogloss dope. It is substantially stiffer, with a weight of .290 Oz.

Deck three is (per Leonard and others recommendation) three layers of 1/32 with nothing but a good coat of Titebond between. I expected this to be the strongest and it is, but it weighs .595 Oz.

I also have three belly pans of similar fabrication.

Pan one 3/32 balsa .240 Oz
Pan two 1/16-CFM-1/32 .295 Oz
Pan three 3 X 1/32 .525 Oz.

Needless to say the three ply/titebonded belly pan is considerably stiffer and stronger than the others, although the two layer carbon fiber version is not far behind in the stiffness department.

I'm spending a lot of money and time on this ship, trying mostly to keep the weight down and the quality of flight up.

I hate the idea of putting .6 of an Oz of basic fabrication weight on the airframe I don't have to, but so many swear by the triple layer laminate. I think these parts are mostly just fairings, but whatever they contribute to fuselage pitch load sharing runs the entire length of the airframe in the case of the belly pan. And it would be senseless to build a super trick plan with outstanding performance only to have it rip the tail off on the first hard corner.

So forumites, which is it? Heavy and stiff/strong to manage the pitch loading or light and adequate to improve performance?

Any suggestions on which parts to use?

Larry (Still building) Lowe

I'd vote for part D: 2 layers of 1/16" glued together with the thinnest possible layer of epoxy..

Actually, I think you will find that even the lightest part will be just fine. Although these parts may feel a little flimsy now, when they are glued in position, "completing the box", and after they are covered with silkspan and finished with dope, they will be more than adequately strong. (The silkspan and dope is another part of the "composite" construction.)

I used part D above (no formers or supports under the molded parts), covered with .56 oz fiberglass cloth (bound with clear nitrate dope), and that covered with silkspan (again prefinished in nitrate) for my last fuselage. It was super strong and quite light.

Gents: I have been making molded balsa parts long before Windy ever thought of it.

Making these is somewhat of a pain up front. A pine block must be carved, and this is where most people give up.

For fuselage turtledecks or wing leading edges, I use two pieces of 1/32" A-grain balsa. Soak in hot water and bend around the form, wrapped with strips of old bed sheet. When dry, they will spring back a little, but that's OK. Soak some silkspan tissue in thinned-out Titebond. Then put the whole thing back together with the silkspan in the middle and again wrap with the cloth sheets around the mold.

This produces the lightest and strongest parts you can imagine.

Why a pine block? Matt uses blue foam. A whole lot easier to carve, and when glued to a base of plywood (slightly undersize) it is more than adequately strong for the task.

Now a question for Larry? How much did the 3 layer balsa piece weigh before the glue? It would seem that either you used an excessive amount of glue, or the wood itself was harder and heaver. We have some 1/32 wood that was quite heavy to start with. Not good for keeping weight down. But I don't really understand the extreme difference in weight, unless the wood was heavy or a lot of glue was used. Or a combination of both. (Remember 12 lb. wood will triple the weight over using 4 lb wood.)

You guys are killing me.

I just picked out my lightest available 1/32 and 1/16 (need to add up to 3/32 and I only want one lamination) stock. Most of it Sig Contest "Very Light", but some of it Midwest.

Generated the proper patterns, soaked in hot water and wrapped to dry.

I will thin out some tightbond, soak the silkspan in that and use that for the laminate layer and we'll see what happens.

Len: Probably a mixture of both. Did not pay close attention to the raw weight of any of the first three, other than to get the lightest wood I had, a mixture of Lone Star and LHS. I confess to slathering on a good amount of titebond and rubbing it into the two layers with my fingers until the entire surface of one side in each layer (three layers, two glue sides) was totally soaked in glue. Like I say, it was stiff when I got done.

I think a combination of the lighter wood, single layer and thinned glue in silkspan as opposed to slathered glue on the wood will give me better results. Will report here when I do.

Whatever the case, this is my 4th set of parts off the mold. One reason to make the plug out of wood, I guess. If I ever get this plane completed I expect to win the perserverance award somewhere...

Onward.

L.

Hey, here's the deal.

One piece molds are always lighter. The strength is really more than adequate. Bog G. and Doug Moon use single layers or 3/32" for the lightest possible pieces, as does Bill W. and Bob Hunt. The laminated forms are stronger but weigh more. Questions is, do you need more strength from your top block?

The answer is usually no. Especially on Noblers.

Does that weight hurt you much? Usually no. Question is, what is your goal? If it is absolutely the lightest airframe, use single layer pieces, they are the lightest. The only alternative is to thinner with laminates, but this is simply not needed, from what I have seen.

>
>You guys are killing me.
>
>I just picked out my lightest
>available 1/32 and 1/16 (need
>to add up to 3/32
>and I only want one
>lamination) stock. Most of
>it Sig Contest "Very Light",
>but some of it Midwest.

Midwest wood is not light. That is probably your 10-12 pound stock (if you are lucky). I got some of that once. Thought it was pretty light until I weighed it. If you do more of these, weigh the wood before gluing just to see how much weight you add with glue.

>Generated the proper patterns, soaked in
>hot water and wrapped to
>dry.
>
>I will thin out some tightbond,
>soak the silkspan in that
>and use that for the
>laminate layer and we'll see
>what happens.
>
>Len: Probably a mixture of
>both. Did not pay
>close attention to the raw
>weight of any of the
>first three, other than to
>get the lightest wood I
>had, a mixture of Lone
>Star and LHS. I
>confess to slathering on a
>good amount of titebond and
>rubbing it into the two
>layers with my fingers until
>the entire surface of one
>side in each layer (three
>layers, two glue sides) was
>totally soaked in glue.
>Like I say, it was
>stiff when I got done.

The extra glue probably also did you in. All you need is a light layer, wiped very thin, and on one piece. You are merely trying to hold the two pieces together so they act as a unit. There is really no tensile strength involved here, so you don't need a lot. Besides, even a very light glue joint is stronger than very light balsa. Anything more just adds weight.

>
>I think a combination of the
>lighter wood, single layer and
>thinned glue in silkspan as
>opposed to slathered glue on
>the wood will give me
>better results. Will report
>here when I do.

Probably true. Keep the weight of the glue down, and even the silkspan will add some strength (although the additional glue needed to hold it together will add some weight.)

Again, weigh the two pieces before and after gluing just to humor us. It is a good reflection on what each component weighs.

>Whatever the case, this is my
>4th set of parts off the mold.
>One reason to make the plug out
>of wood,

It still wouldn't be needed. Even the foam plugs hold up to multiple moldings.

>>Whatever the case, this is my
>>4th set of parts off the mold.
>>One reason to make the plug out
>>of wood,
>
>It still wouldn't be needed.
>Even the foam plugs hold
>up to multiple moldings.

Len:

Please. Don't let the air out of my ballon. I've gone to some effort to carve the balsa in the kit to the right size, minus 3/32 to form a rigid plug for the shell. Let me think that was at the least, not wasted effort. Works good, even if overkill.

>Len:
>
>Please. Don't let the air
>out of my ballon.
>I've gone to some effort
>to carve the balsa in
>the kit to the right
>size, minus 3/32 to form
>a rigid plug for the
>shell. Let me
>think that was at the
>least, not wasted effort.
>Works good, even if overkill.
>
>
>

If you carved it out of balsa, that isn't too bad, although it can be a waste of good balsa. Some try to carve the plugs out of pine, and that gets tedious, especially for a small number.

By the way, when making the plug out of foam, attach it to an undersize piece of plywood for rigidity. Then cut "former" slots in the foam at appropriate places and make a plywood "former" at these locations of the appropriate shape. Then all you need to do is carve/sand it down to the "formers" and you will have the "perfect" shape for your plug.

You want the turtle daeck strong? Place a former at the front where the canopy will be. You know the pilots back. And a teeny tiny one at the rear. Once these are in place you will see that your SINGLE PIECE is plenty strong. Then glue it down with medium ca one side at a time. Make the fuse stronger so you arent relying on the turtle deck for strength. One way to make sure of this is to get some very very light 1/16 and place it all along the top of your fuse with thin CA from a dropper. Now you have created the box before putting on the turtle deck. It will be ther just adding more strength and you will not have increased the weight.

I use single layer 3/32 on all the top and bottom of my big bear at 720sq in. With the top crutch method inside the top of the fuse it is plenty strong and that plane still only weighs 58oz.

I have been taught all my life build light build light build light. I have always been building planes that demand light building in order to fly well. I have used single layer 1/16 for top and bottom blocks. This did not hold up after about 350 flights the nose was gone. Shaking horribly. And finally the wing buckeled. A one season airplane for sure. Broke at the last contest of the season. Since I have gone to 3/32 single layer I have one plane pushing 1200 and still no signs of wear on the toop block. The bottom has a few cracks but these were caused by dropping the plane once and few hard landing is the wind, fuse gear. These started cracks that are only getting bigger with time.

I have built two planes with laminated 1/16 bottom blocks and saw absolutley no advantages of all the extra work involved. Except for more room on sanding.

A major disadvantage to laminated 1/16 is that if it get glued on crooked and you force to be straight it is strong enough to warp your fuse. It will twist your fuse. I know this frm experience. It has to be cut off and rebuilt. The molded balsa is way stronger than you think once it is attached. Especailly if it is laminated.

Time and time again I hear of this glassing the nose or fuse and just dont get that approach at all. The structure most be strong from the inside out to perform. Not the outside in. Covering provides strength sure I know this but when you rely on it and factor it in as a part then you can develop internal problems and not know it. Cracks come from the inside. By the time they get to glass reinforcing it is too late. So what's the use. Just build it stronger with light weight balsa on the inside and save on weight in the long run bypassing all that glass work.

Building the fuse as a full box before blocks are added will yeild a light stong fuse. I have 1/8 matched sides from sig. From F3(back of the wing) at the top I have a peice of 1/20 balsa cut to the exact shape of the fuse from the top veiw. I place this up against F3 and it tappers along with the fuse and glued in with thin CA from a dropper all the way back. Then the fuse is turned over and the balsa 1/8 formers are dropped in place. Then in my case a pipe floor is added and cross bracing between F5 and F6 and the tail wheel mount and the end of the fuse. Now you use 3/32 top blocks all day long and it wont be heavy and it WILL be strong. Also with the top crutch piece you dont have to have a jig to build the fuse staright. It will follow that tapper and as long as you get it on the former F3 staright it will be staright. By the way I leave that piece on the top solid I dont not go back and cut it out. You will cut the strength right out of it. It is only 1/20 it doesnt show up on my gram scale.

I have built it many many ways trying to get it light and strong enough. The above is working very will so far and is by far the lightest to strength ratio I have found.

Staight is objective 1
Strong is objective 2
Light is objective 3

Laminated woods with all that glue are never going to be light that is a fact. So figure a way to get the structure strong from the inside out then the rest is a cake walk.

By the way finish it with a scale on the table this is the best place to save on weight not the structure itself.

Doug,

There is a lot of good information in your post. I plan on doing the same as you with the 1/20th sheet, but I thought I might just do it from 4" pieces joined cross grain. I know it's just a little more weight, but there is a really significant strength and twisting advantage with the cross grain orinetation of the top aft fuselage crutch.

I'm told that for strength, you shouldn't use anything but epoxy resin with glass cloth. But I used nitrate dope as the binder, and it seems incredibly strong. The surface "seems" stiffer than my classic Roadrunner fuselage was (silkspan/dope finish, very soft carved/hollowed balsa blocks), but the newer fuselage has some benefit of structure.

I actually measured and logged the weight gain in a full sized fuselage, added by the fiberglass/silkspan/nitrate pre-finish. It was .7 ounces total. By prefinish, I mean filled and ready to paint the color coat, from an initial state of raw balsa.

[photo not recovered: 3d61490b68916215.jpg]

The total prefinished fuse weight was 7.65 ounces. That included rudder, cowl, and molded belly pan, ready to add the canopy details. This fuselage is just over 41 inches long and 2.5" wide at the wing root. It has 3/32" fuse sides, 1/32" plywood nose doublers, 2 layers of laminated 1/16" molded balsa for top, bottom, and nose blocks. The aft fuselage formers are tilted ("geodesic"), with about .1" of convex curvature shape, and the formers are laminated from 1/16" and 1/32" balsa.

[photo not recovered: 3d614a726a1c3ff6.jpg]

It might have weighed a little less, but I carved the cowl block and left it a little hefty - a molded fiberglass one would be lighter, I believe. And I could have selected some lighter wood for the molded blocks.

(We'll see how it holds up..)

Larry looks great. When will it be done? Be careful of that bottom cowl. It might not keep your pipe cool. Experience has told be that the first hole the air finds after it goes in the cowl is the where it exits. If you are getting irregular runs at the beggining then try some packing tape on the inside so it looks the exact same over the slots excpet for the ones aft the belly of the pipe. However you may have this setup already working in another ship.

Just thoughts

Hi Doug,

You bring up a good subject. And one I am basically completely ignorant about: getting proper cooling with a pipe. AFTER I made up this removable belly pan, I decided that not only was it not necessary to have it removeable, but that I also should just have a simple open hole on the aft portion, like I see on some planes (e.g. Bill Werwage's). (I still have the mold, could easily make up a different version.)

Meanwhile, I'll try your suggestions about blocking off holes if I have problems.

I'd be very interested in your setup on this! I can easily change it (and will).

I know you are getting great runs on your piped motors, obviously good enough to get a 5th at the Nats.

Best regards,

Larry,

I actually built air-scoops into my cowling that are pointed directly at the header. Look on the ultra hobbies web site. You can see one of them on my plane it's the very bottom one on the right side. It's a little hard to see due to the angle but is definitely build into the cowling.

>I actually measured and logged the
>weight gain in a full
>sized fuselage, added by the
>fiberglass/silkspan/nitrate pre-finish. It was .7
>ounces total. By prefinish, I
>mean filled and ready to
>paint the color coat, from
>an initial state of raw
>balsa.
>

OK, OK, please elaborate.

We have been logging some finishes (only one real good one, though). The lightest has been with clear dope and zinc stearate filler with one "guide coat" of very thin auto primer (this is used for shadowing). This was used on Doug's Big Blue Billy Bear.

.7 oz is half of what we got.

I would like to know this method.

It wasn't TOO elaborate..

Brushed on, unthinned clear nitrate dope applied over .56 oz SIG glass cloth over the entire fuselage. Light sanding to trim edges. Another brushed on coat or two of nitrate clear over that, then covered with medium grade silkspan.

Thinned clear nitrate with industrial talc filler, sprayed on. Wet sanded with Prep Sol I. Repeated 2 or 3 times, sanding away almost all of what what applied. (It fills very quickly..)

At that point it is ready (for ME) to paint the color coat (auto lacquer, Dupont Lucite).

Maybe I'm not as picky with my prefinish as I might be?

My scale is an Ohaus digital, reads to .05 ounce. I balanced the fuse and parts on their nose on the scale for the readings. It may not be accurate or something?

Here's a couple more photos that show my "ready for color" prefinish. It might not be as ready as others are used to..

[photo not recovered: 3d62a276448b9ebd.jpg]

Notice, they aren't in silver or anything!

[photo not recovered: 3d62a2be44dd9ebd.jpg]

(Pink Panther pilot; Cookie Monster was fired after he crashed my beautiful yellow Shogun..)

And notice, you can SEE wood through it (I sand most of the filler coat away..). My standards for prefinish may be sub-standard.

I just re-weighed the entire ship, which has the base color on it, with Aero .51, header, coupler and pipe, 8 ounce plastic tank, 3B CF prop, 2" Tru Turn Spinner. Still needs trim colors and clear, and leadout ends. It is 3 lb 8.75 oz (56.75 oz, right?) I'm hoping for 60 ounces or less dry finished weight, wingspan is 60 inches. It'll probably end up heavier than that.

LAST EDITED ON Aug-20-02 AT 05:55 PM (CDT)

Intrepid XL? Gorgeous! Your paint and finish are way out of my league.

I do see a little "hicky" on the lower side of the nose..

Good idea, I'll keep it in mind. It would be pretty easy to add scoop or NACA duct openings in my belly pan if I remake it.

Great looking airplane, Jim.

(Clearly you Alabamians are quite good at this model airplane stuff..)

Best regards,

L.

PS

Thought I would at least get a rise, referring to you as a Texan, Jim.. (I changed it back..)

I don't have anything against you refering to me as a Texan,
My Uncle, Aunt and Cousin's are Texans. One cousin lives in Alabama with me now, the other one lives in Irving Texas, whom I visit when I am there flying. My Grandmother was born in Cleburn Texas and My Father, Mother and Grandfather were born just across the Red River in Wardville and Ardmore, OK. So I do have a lot of Texas and Oklahoma connections.

I generated two more sets of parts and finally got results I am happy with.

Brodak Nobler Turtledeck

Num Weight Fabrication
1 .180 Oz - 1/32 Sheet over original plug
2 .290 Oz - 2 X 1/32 Sheet Carbon Mat Lamination/Dope
(Plug modified to include base of rudder)
3 .595 Oz - 3 X 1/32 sheet Slathered with Titebond
4 .270 Oz - 1/32 & 1/16 Silkspan soaked in thinned TB
5 .280 Oz - 1/16 with edge stiffeners

Brodak Nobler Belly Pan

Num Weight Fabrication
1 .240 Oz - 1/32 Sheet
2 .295 Oz - 1/32 & 1/16 Sheet Carbon Mat Lamination/Dope
3 .525 Oz - 3 X 1/32 sheet Slathered with Titebond
4 .430 Oz - 1/32 & 1/16 Molded not laminated
5 .200 Oz - 1/32 Sheet (Best Stock)

New Results:

Turtledecks:

#4: The 1/32 and 1/16 turtledeck templates were shaped over one another and allowed to dry. Light silkspan was soaked in a 50/50 mixture of water and tightbond and layered on the internal 1/32 then the 1/16th outer shell was wrapped back in place. Outstanding light laminations although the final part was not quite formed the way I would like. Clearly VERY LITTLE GLUE is required. Soaking the silkspan in the thinned glue is the way to laminate layers if you are going to go that route.

Leonard: The two templates of 1/32 and 1/16 sheet stock weighed a combined .275 Oz when loosely trimmed prior to molding. After molding and laminating with the silkspan in the glue, final trimming was done to the exact outlines of the part. Which resulted in a final weight of .270 Oz, .005 less than the part templates before forming. So a LOT of excess weight was in the glue I used. The silkspan shrank slightly as it dried, closing up the shell. Once this part was glued in place it would almost certainly be the strongest of the bunch other than the hidiously heavy triple laminate version.

#5: My lightest piece of stock was 1/16th so I put a simple template of that on the form, but laminated a 1/32 strip along the lower edge where the part meets the fuselage, tapered to nothing. This came out with a nice shape, although a bit of titebond glued the plug to the part and a bit of the plug ended up on the part. This weighed very slightly more, due to the poor choice of wood for the edge thickeners, I suspect. It gave me the finest overall formed part, which I think I will use. The lightest part, number 1, does not include proper forming fairing into the vertical fin, so it is not usable.

Belly pan:

#4: The belly pan was formed from two templates 1/32 inner and 1/16 outer, and allowed to dry with the intention of using the highly successful soaked silkspan method of lamination. The parts off the mold weighed a combined .430 Oz, however, and this attempt was abandoned because the weight of the raw materials was too high.

#5: My lightest 3/32 sheet stock was used, no lamination or other hassle and the result was the best part for the belly in shape and the lightest by a good margin at .200 Oz.

Using the number 5 turtle deck and number 5 belly pan at a total of .480 Oz, I will save .640 Oz over the triple laminated versions that total 1.12 Oz.

Conclusions:

For turtledecks, belly pans, fuselage tops and the like, go get the lightest 3/32 stock you can possibly find and mold it in one operation. Paying attention to stock parts weight is most of the issue here as soft 3/32 is just a lot more workable during molding/trimming and once secured on the fuselage and finished with whatever laminations and finishing, will be stiff/strong enough. I have a huge box crutch in the 'zoot suit' so I am not worried about strength, just shape. Lamination is not worth the hassle here, as far as I am concerned.

For situations where the part is more structural, like, say, the 1/16th leading edge of the next Nobler I build, where I intend to leave off the 1/4 square LE part and just make the leading edge and the spar a big 1/16th D tube, then two layers of really light, soft 1/32 laminated with the silkspan soaked in 50/50 Titebond or White glue and Water is clearly the right answer. The weight cost of this form of lamination is microscopic, less in my case than the weight of the trimmed excess from the formed balsa to the final part. And it is certainly as strong and stiff as the carbon fiber/dope method, and certainly a lot cheaper.

Final conclusion is that it's worth doing a part over and over again until you get it right. When I was a kid I wanted to get flying, so I put the fastest parts I could build together as quickly as I could. This molding exercise has tried my patience, but I am satisfied I have done enough to (a) have acceptible quality parts for this model and (b) have learned enough to know what techniques to apply to the second one which ought to benefit from a lot I have learned on this one.

I cannot stress how much difference there is in various quality wood, diffence it is hard to notice when handling small or thin parts. The Sig "Contest Light 4-6 Lb" balsa was hidiously heavy in comparison to some Lone Star quality balsa and even that varied considerably in weight.

And glue can add an enormous amount of unneeded weight. I love how fast CA glue dries and how the thin stuff I use from Model Research wickes right up into the balsa, but it does add weight and I am now certain I am using way more glue all over the structure than I really need.

At some point, however, close enough is close enough and I need to just take the best of the parts I have and get this thing flying.

It's already probably better than I can learn to fly when I finally restart, and I can build a better one while I am flying this one.

Onward.

And thanks for the suggestions from the forumites.

Larry (Enough zoot is enough) Lowe

Jim,

Actually, for some reason I was thinking that the photos on the Ultra Hobby site were all "Texans at the 2002 Nats". Then I remembered that you are from Alabama, and corrected it.

Although we New Mexicans give Texans a hard time, we like'em just fine. (Even if the poor dears haven't got access to any decent green chili..)

Your ship is gorgeous, I don't doubt it is a great flyer too.

L.

PS

Our CL flying field in Las Cruces is a street over from the Joy Canning company. They pull in there a couple of times a day with 18-wheelers loaded with green chili (mostly from Hatch).

The smell of that green chili cooking is heavenly.. My wife just brought home 30 lbs of it, roasted, which we put up.

That and onions. Man, Las Cruces smells good this time of the year..

>
>That and onions. Man, Las Cruces
>smells good this time of
>the year..

Maybe it's just the fact that I'm from Arizona.

Or has this thread wandered well off topic?

Larry (Weigh All The Balsa) Lowe

Larry,

Please forgive me, I'm an idiot, but I'm fascinated. What is that wing treatment? It looks like balsa sheeting - is it? It looks too smooth to be anything else. Is the wing foam? I can tell that all these other guys already know the answer, but I'd appreciate an "inside glance" at how the "big boys" do things. This plane is totally cool, by the way.

Nice pilot, too! (ba-dum ba-dum, de-dum, d-dum d-dum d-dum d-dum d-daaaaaaaaaaaaaaa!)

Hey, in my case, "big boy" is literal!

The wings are conventional balsa framed. Medium weight silkspan over open bays. They look a little white because the filler coat (clear nitrate and non-perfumed talc) makes it look like that.

Here's the very wing, underside..

[photo not recovered: 3d6441e766133357.jpg]

Here's a couple more shots of Pink..

[photo not recovered: 3d6442c26730d9a9.jpg]

and

[photo not recovered: 3d6440aa650f63b7.jpg]

You'll notice that Pink has one hand up, judging the size of the triangle he's flying.. Cool, he is.

Yes. It has. Sorry.

Hey Larry, I really appreciate your trying stuff out and actually presenting data instead of arm waving. I may never make a molded part, but if I do, it will work better because of your experiments. Having better airplanes is more fun.

> Hey Larry, I really appreciate your
> trying stuff out and actually
> presenting data instead of arm
> waving.

Thanks.

Often times I ask a question and end up with a dozen different answers, describing a half dozen points of view and no real understanding of what the right answer is. Opinions being like, well, you know...

Certainly, a fair amount of what we do is subjective and I firmly believe that crafting a good stunt plane is as much art as science.

But even at that, the only way to sort out good art from bad art is to do enough documentation and comparison that your results can speak for themselves. God knows I never had the patience as a kid to do any of that.

I am convinced that the SSWF can become an absolute first class repository of quality answers to a lot of fundamental questions if more folks take the time to document processes and think of each contribution to the 'community memory' as such.

Larry (too many questions, not enough answers) Lowe

>
>>
>Some try to carve the
>plugs out of pine, and
>that gets tedious, especially for
>a small number.
>
>>
>Leonard Neumann

I recently made a fir plug for my Fancy Pants deck. It took
35 minutes using a table saw, sureform pland and belt sander.

The deck was made of medium weight 1/16 balsa (nne sheet).

After 10 flights, it has developed a helical split along the top radius.

It could be that it wasn't fully down on the body frames.

A foam core would be a problem to me, since foam is soluable
in most of my adhesives and paints.

Rex

You glue the foam core to a piece of plywood for stability, but beyond that there is no glue or paint. Regular Titebond or epoxy will glue it fine. All you use it for is a plug to glue the top.

Queston on your deck that developed the cracks, did you use any ammonia while bending it? Ammonia will make the wood brittle. If not, was the wood wind checked? Some of the lighter wood will show wind checks, which makes it unsuitable for anything like this or anything else that is structural. This is one of the benefits of using multiple layers (two or three layers of 1/32). The layers, even though the grain is in essentially the same direction, will act somewhat like plywood in adding strength and keeping it from splitting.

Once again, my conclusion is that if you go to a single layer, get the lightest, dead soft 3/32 you can find. Soak it good and long in the hottest water you can get it in. It will form easier and is easier to trim after than laminated parts. Then put a quality outside finish on it. Let the silkspan, glass, dope or whatever give you the stiffness, not the balsa. That should prevent splits.

Thin (1/16 or less) wood that is less than contest light and cut through the grain the right way is asking to split. But an internal layer of silkspan soaked in thinned Titebond will turn two thin, flimsy eggshells in to a light, stiff laminated aircraft component. Again, light material with the cut the right way through the grain is imperative.

Rex's post reminds me to use my own advice and I will incorporate turtledeck number 4 in my ship rather than 5, which turned out slightly nicer from a shape point of view, but is only 1/16 thin. Part 4 has the lamination to ensure it does not split, particularly with the tight bend at the top.

Plus which I save .010 Oz.

Larry (never know when to quit) Lowe